In a historic speech to both houses of US Congress, German Chancellor Angela Merkel called on the world's biggest carbon dioxide polluter to join international efforts against global warming.

Merkel met with US President Barack Obama at the White House on Tuesday before her speech on Capitol Hill as the second German leader to address Congress since Konrad Adenauer in 1957.

The German leader, who began her second term at the helm of a new coalition last week, stressed that hr country would never forget American help in brining down the Berlin Wall — less than a week before the 20th anniversary of the historic event.

"Ladies and gentlemen, to put it in just one sentence, I know, we Germans know, how much we owe to you our American friends. And we shall never, I personally shall never, ever forget this," Merkel said.

She went on to urge world leaders to 'tear down the walls of today', and step up efforts to reach binding commitments on battling global warming.

She also reiterated Germany's commitment to the war in Afghanistan — in a reassuring gesture to Washington.

Her remarks come about two months after a disastrous NATO airstrike called by a German commander that killed scores of civilians and fledgling public support of the mission,.

Obama praised the two countries' close ties and said he had come to understand the significance of Merkel's environment campaign.

"The United States, Germany, and countries around the world I think are all beginning to recognize why it is so important that we work in common in order to stem the potential catastrophe that could result if we continue to see global warming continuing unabated," Obama said.

ZHD/AKM